function diff = J_0_fun(m,param)

    diff = - 2.*param.c.*(1-param.alpha)./param.sigma^2./(param.gamma_R_2-param.gamma_R_1).* ...
        ((1./(1-param.alpha)-param.gamma_R_1).*m.^param.gamma_R_1.*int_rep1_fun(m,param) ...
        -(1./(1-param.alpha)-param.gamma_R_2).*m.^param.gamma_R_2.*int_rep2_fun(m,param));

end